Common types of printers include single-pass systems and shuttle-based systems. FIG. 1A illustrates an example of a single-pass system implemented on a printer. One or more printheads span the width of the printer. A “width” of a printer refers to the range of a printing area in a direction perpendicular to the direction of the paper transport (i.e., downstream direction). The printheads can access reservoirs of cyan-, magenta-, yellow-, and black-colored ink. An image is printed on a medium by advancing the medium downstream under the arrangement of printheads that eject ink onto the medium. An “image” refers to any visually perceptible object (e.g., a document, a banner, a graphic) that can be recorded on a “medium,” which is a physical substrate (e.g., paper or tile) upon which the image can be permanently or temporarily recorded. Moreover, an “image” may refer to a portion of another image. The printheads can dispense different colored inks at the same time to print a colored image.
FIG. 1B illustrates an example of a shuttle-based system (i.e., a multi-pass system) implemented on a printer. Here, printing involves multiple “passes” of a printer carriage that moves perpendicular to the downstream direction. The carriage includes printheads. With each pass, ink can be dispensed onto the medium to print an image. As such, the carriage may need to pass the printheads over the medium multiple times to produce full-color results.
Systems for inspecting images being printed have long been a tool employed to ensure acceptable print quality. Common inspection systems use line sensors or area sensors that capture a sample image of a printed image. This captured image can be analyzed to check print quality. For example, FIG. 2A illustrates an example of a line sensor that spans the entire width of a printer. FIG. 2B illustrates an example of a line sensor that does not span the entire width of the printer but includes optics that can capture the entire width of the printer. Lastly, FIG. 2C illustrates an example of an area sensor that captures an area of an image being printed. High-speed printing presses and single-pass inkjet systems commonly use a stationary two-dimensional still camera to capture images of a printed image. However, wide-format printers require such a large camera that it is impractical and cost-prohibitive to implement such systems.